Indirect Fluorometric Determination of Lactic Acid in Wine

Abstract

Abstract A sensitive, specific, and reliable fluorometric method for the determination of lactic acid in wine is described. After the wine sample was boiled and diluted, lactic acid was fluorometrically determined by evaluating the concentration of fluorophore derived from the reaction between acetaldehyde, a product of the oxidation of lactic acid, and 1,3-cyclohexanedione. The best oxidation conditions were a temperature of 90°C for 2 min and a Ce(SO4)2 concentration of 2 mg/mL in 0.5M H2S04. These values are not strictly critical, because the time value ranged from 1 to 2.6 min, temperature from 82 to 93.6°C, Ce(SO4)2 concentration from 1 to 2.6 mg/mL, and H2SO4 concentration from 0.125 to 0.72M; the values yielded fluorescence intensity decrements of <5% relative to the optimum. Six wine samples (3 red and 3 white) as well as those spiked with 1 and 2 g lactic acid/L were analyzed. The average recoveries ranged from 98.3 to 100.1%, with the relative standard deviation ranging from 1.3 to 3.4. The results of the fluorometric analyses compared with those obtained from the known liquid chromatographic method gave good agreement. The proposed method appears to be sensitive, specific, and reliable but not advantageous for routine analysis.